Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $201.46   8.523%   $218.6304   $218.63   $218.65   $218.60  
  Purchase #2 $132.53   8.689%   $144.0455   $144.05   $144.05   $144.00  
  Purchase #3 $196.95   4.653%   $206.1141   $206.11   $206.10   $206.10  
  Purchase #4 $67.33   13.599%   $76.4862   $76.49   $76.50   $76.50  
  Purchase #5 $39.95   5.795%   $42.2651   $42.27   $42.25   $42.30  
  Purchase #6 $103.53   13.454%   $117.4589   $117.46   $117.45   $117.50  
  Purchase #7 $194.82   12.451%   $219.077   $219.08   $219.10   $219.10  
  7 purchase totals = $936.57       $1,024.0772   $1,024.09   $1,024.10   $1,024.10